Hello guys I'm going to be brief since I've got 3 problems that I cannot (obviously) solve by myself.
1) When I halt my machine the screen stays on (just the backlight with a black screen) without really shutting down.
2) I've got 2 function keys that can dim the brightness of my screen but they aren't working. How can I set 'em up?
3) If I give emerge -DuNav world... this is what I get. How can I solve those blocked packages?

!!! Multiple package instances within a single package slot have been pulled
!!! into the dependency graph, resulting in a slot conflict:

sys-auth/polkit:0

(sys-auth/polkit-0.107-r1::gentoo, ebuild scheduled for merge) pulled in by
(no parents that aren't satisfied by other packages in this slot)

(sys-auth/polkit-0.110::gentoo, ebuild scheduled for merge) pulled in by
>=sys-auth/polkit-0.108 required by (sys-fs/udisks-2.0.91::gentoo, ebuild scheduled for merge)

sys-apps/hwids:0

(sys-apps/hwids-20121119::gentoo, installed) pulled in by
(no parents that aren't satisfied by other packages in this slot)

(sys-apps/hwids-20130108::gentoo, ebuild scheduled for merge) pulled in by
>=sys-apps/hwids-20121202.2[udev] required by (sys-fs/udev-197-r2::gentoo, ebuild scheduled for merge)

virtual/udev:0

(virtual/udev-171::gentoo, ebuild scheduled for merge) pulled in by
~virtual/udev-171 required by (net-wireless/bluez-4.99::gentoo, ebuild scheduled for merge)
<virtual/udev-196 required by (sys-fs/lvm2-2.02.88::gentoo, installed)
(and 1 more with the same problems)

(virtual/udev-196::gentoo, ebuild scheduled for merge) pulled in by
=virtual/udev-196[gudev] required by (xfce-base/thunar-1.4.0::gentoo, ebuild scheduled for merge)
>=virtual/udev-196[gudev,hwdb] required by (sys-fs/udisks-2.0.91::gentoo, ebuild scheduled for merge)
(and 22 more with the same problems)

It may be possible to solve this problem by using package.mask to
prevent one of those packages from being selected. However, it is also
possible that conflicting dependencies exist such that they are
impossible to satisfy simultaneously. If such a conflict exists in
the dependencies of two different packages, then those packages can
not be installed simultaneously.

For more information, see MASKED PACKAGES section in the emerge man
page or refer to the Gentoo Handbook.

The following keyword changes are necessary to proceed:
#required by gnome-base/gvfs-1.12.3-r1[udisks], required by xfce-base/thunar-1.4.0[dbus,xfce_plugins_trash], required by xfce-extra/tumbler-0.1.25, required by @selected, required by @world (argument)
=sys-fs/udisks-2.0.91 ~amd64
#required by sys-fs/udisks-2.0.91, required by gnome-base/gvfs-1.12.3-r1[udisks], required by xfce-base/thunar-1.4.0[dbus,xfce_plugins_trash], required by xfce-extra/tumbler-0.1.25, required by @selected, required by @world (argument)
=sys-auth/polkit-0.110 ~amd64
#required by sys-fs/udev-197-r2[hwdb], required by virtual/udev-196, required by x11-base/xorg-server-1.13.1, required by x11-drivers/ati-drivers-12.11_beta11, required by @selected, required by @world (argument)
=sys-apps/hwids-20130108 ~amd64
#required by sys-fs/udev-197-r2[openrc], required by virtual/udev-196, required by x11-base/xorg-server-1.13.1, required by x11-drivers/ati-drivers-12.11_beta11, required by @selected, required by @world (argument)
=sys-fs/udev-init-scripts-19 ~amd64

The following USE changes are necessary to proceed:
#required by virtual/udev-196, required by x11-base/xorg-server-1.13.1, required by x11-drivers/ati-drivers-12.11_beta11, required by @selected, required by @world (argument)
=sys-fs/udev-197-r2 gudev hwdb
#required by virtual/udev-171, required by net-wireless/bluez-4.99, required by dev-libs/openobex-1.5[bluetooth], required by app-mobilephone/obex-data-server-0.4.5, required by gnome-base/gvfs-1.12.3-r1[bluetooth], required by xfce-base/thunar-1.4.0[dbus,xfce_plugins_trash], required by xfce-extra/tumbler-0.1.25, required by @selected, required by @world (argument)
=sys-fs/eudev-0 gudev hwdb

Use --autounmask-write to write changes to config files (honoring CONFIG_PROTECT).

!!! Multiple package instances within a single package slot have been pulled
!!! into the dependency graph, resulting in a slot conflict:

virtual/udev:0

(virtual/udev-171::gentoo, installed) pulled in by
=virtual/udev-171 required by (sys-fs/eudev-0::gentoo, installed)
<virtual/udev-196 required by (sys-fs/lvm2-2.02.88::gentoo, installed)
(and 1 more with the same problems)

(virtual/udev-196::gentoo, ebuild scheduled for merge) pulled in by
=virtual/udev-196 required by (virtual/dev-manager-0::gentoo, installed)
>=virtual/udev-196[gudev,hwdb] required by (sys-fs/udisks-2.0.91::gentoo, ebuild scheduled for merge)
(and 22 more with the same problems)

It may be possible to solve this problem by using package.mask to
prevent one of those packages from being selected. However, it is also
possible that conflicting dependencies exist such that they are
impossible to satisfy simultaneously. If such a conflict exists in
the dependencies of two different packages, then those packages can
not be installed simultaneously.

For more information, see MASKED PACKAGES section in the emerge man
page or refer to the Gentoo Handbook.

!!! Multiple package instances within a single package slot have been pulled
!!! into the dependency graph, resulting in a slot conflict:

virtual/udev:0

(virtual/udev-171::gentoo, installed) pulled in by
<virtual/udev-196 required by (sys-fs/lvm2-2.02.88::gentoo, installed)

(virtual/udev-196::gentoo, ebuild scheduled for merge) pulled in by
>=virtual/udev-180 required by (sys-fs/eudev-1_beta1-r2::gentoo, ebuild scheduled for merge)
=virtual/udev-196[gudev] required by (gnome-base/gvfs-1.12.3::gentoo, installed)
(and 23 more with the same problems)

It may be possible to solve this problem by using package.mask to
prevent one of those packages from being selected. However, it is also
possible that conflicting dependencies exist such that they are
impossible to satisfy simultaneously. If such a conflict exists in
the dependencies of two different packages, then those packages can
not be installed simultaneously. You may want to try a larger value of
the --backtrack option, such as --backtrack=30, in order to see if
that will solve this conflict automatically.

For more information, see MASKED PACKAGES section in the emerge man
page or refer to the Gentoo Handbook.

you might want to look around the forums for the brightness keys .. may depend on the keyboard type .. check kernel settings too .. proper keyboard driver for X helps too my own keyboard are autodetected

.. monitor not dim-iing sounds like a monitor settings issue in the monitor itself .. does it have a menu feature? check the time-out for screen blanking/sleeping .. all newer monitors have auto-sleep features .. but sometimes they can be miss - set.

sorry I have rarely fought with these issues but the forums have dealt with these matters in the past .. used advanced search .. :^)

check your screensaver settings .. also try to look at kernel x86 hardware modules (generally for laptops) some although named for a manufacturer are semi-generic since chipsets are often similar .. if you have them compiled as modules eudev/udev may detect and auto load them ..

Check for back light control setting in kernel as well under acpi (screen) settings and graphic devices LCD backlight support